JP2015150842A - Biaxially-stretched polyamide film, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially-stretched polyamide film excellent in tear properties and particularly in straight line-cuttability and excellent in pinhole resistance and particularly in flex pinhole resistance.SOLUTION: The biaxially-stretched polyamide film is obtained by using a mixture of aliphatic polyamide with polymetaxylene adipamide (MXD6). When a packaging bag is obtained by using a film laminate obtained by laminating the biaxially-stretched polyamide film, an incision is made on the packaging bag in the longitudinal direction (MD direction) of the biaxially-stretched polyamide film when produced, and the packaging bag is torn by 200 mm in the MD direction, the biaxially-stretched polyamide film is characterized in that the deviation width of a torn part of the film laminate between the front surface thereof and the back surface is 2.0 mm or less. A mixing ratio of the aliphatic polyamide with MXD6 satisfies the expression: (the aliphatic polyamide)/MXD6=80/20-99/1 (by a mass ratio). The method for producing the biaxially-stretched polyamide film comprises a step of stretching an unstretched film simultaneously and biaxially by 2.5 or higher vertical stretch ratio and 7 or higher vertical×horizontal stretch ratio.

Description

  The present invention relates to a biaxially stretched polyamide film having excellent tearability and pinhole resistance.

  Polyamide films such as nylon 6 have excellent tensile strength and impact resistance, and are therefore widely used in packaging applications such as foods, pharmaceuticals, and industrial products.

  However, since a resin film containing a polyamide film generally has poor tearability, a method for improving the opening property of a packaging bag using various films has been proposed. For example, there is a method of making a notch, but when it is torn, it may not be torn linearly or the tearing resistance may be increased, which may cause troubles such as spilling the contents. Further, there is a method of inserting an opening tape into the opening portion, but there are problems such as equipment for opening the tape, productivity, and cost increase.

  On the other hand, there is a uniaxially stretched sealant film in which polyethylene or polypropylene sheet is stretched in one direction as a product that gives the film itself a linear cut property. May remain as a foreign object.

  Further, a polyamide film in which MXD6 or the like is mixed with polyamide 6 to impart tearing properties is known, but the linear cut property is insufficient (for example, Patent Document 1).

JP-A-7-1113015

In contrast, the present inventors have found the following.
The polyamide film having excellent straight-cut properties as described in Patent Document 1 has MXD6 dispersed in polyamide 6 incompatible with each other, so that MXD6 dispersed in the sea made of polyamide 6 does not mix evenly. The MXD6 distributed in the shape of islands is oriented in a long rod shape in the longitudinal direction (MD direction) of the film formation by stretching, and the polyamide film 6 having a weak interaction when the obtained polyamide film is torn in the MD direction. It is considered that tearing is developed by the continuous progress of peeling at the interface between the surface and MXD6. Therefore, it is necessary to orient MXD6 more strongly in order to improve the linear cut property. Also, these polyamide films are usually used as packaging bags after being laminated. Since the packaging bag is used as a half-folded state of the film, that is, as a three-sided bag, when the orientation of the polyamide film is weak or angularly misaligned with respect to the MD direction, the half-folded polyamide film is It may act in the direction which inhibits each other's linear cut property, and as a result, the tearability as a packaging bag may be impaired.
On the other hand, the MXD6 has a rigid structure compared to the polyamide 6, and mixing the MXD6 with the polyamide 6 for the purpose of imparting a linear cut property tends to impair the flexibility of the obtained polyamide film. The pinhole resistance of the polyamide film, particularly the bending pinhole resistance, may be lowered.
An object of this invention is to provide the biaxially stretched polyamide film excellent in tearability and pinhole resistance.

The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems.
That is, the gist of the present invention is as follows.
(1) A biaxially stretched polyamide film comprising a mixture of an aliphatic polyamide and polymetaxylene adipamide (MXD6), wherein a packaging bag is obtained using a film laminate obtained by laminating the biaxially stretched polyamide film After that, a notch is made in the longitudinal direction (MD direction) when forming the biaxially stretched polyamide film, and the gap width between the tear portions of the front and back surfaces of the film laminate when it is torn 200 mm in the MD direction is 2.0 mm. A biaxially stretched polyamide film characterized by:
(2) The mixing ratio of aliphatic polyamide and polymetaxylene adipamide (MXD6) is aliphatic polyamide / polymetaxylene adipamide (MXD6) = 80/20 to 99/1 (mass ratio). A biaxially stretched polyamide film as defined in (1).
(3) The biaxially stretched polyamide film according to (1) or (2), wherein the unstretched film is simultaneously biaxially stretched at a longitudinal stretching ratio of 2.5 times or more and a longitudinal x lateral stretching ratio of 7 times or more. Manufacturing method.
(4) The method for producing a biaxially stretched polyamide film according to (3), wherein the stretch ratio in the machine direction (MD direction) and the stretch ratio in the transverse direction (TD direction) are MD direction / TD direction ≧ 0.91.
(5) The method for producing a biaxially stretched polyamide film according to (3) or (4), wherein the tenter is driven by a linear motor system.
(6) A packaging bag using the biaxially stretched polyamide film of (1) or (2).

  According to the present invention, a biaxially stretched polyamide film having excellent tearability and pinhole resistance can be obtained.

It is a schematic diagram which shows embodiment of the packaging bag in this invention. (A) is a three-sided bag, (b) is a four-pack, and (c) is a self-supporting bag. In the present invention, tearability was evaluated in the form of (a). It is a figure which shows the shape in the three-way bag which evaluated tearability of this invention.

  Examples of the aliphatic polyamide used in the present invention include nylon 6 using ε-caprolactam as a main raw material. Examples of other polyamide resins include polyamide resins obtained by polycondensation of lactams having three or more members, ω-amino acids, dibasic acids and diamines.

  Specific examples of lactams include enantolactam, capryllactam, lauryllactam, and the like in addition to the above-described ε-caprolactam. Examples of ω-amino acids include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, and 11-aminoundecanoic acid. Dibasic acids include adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecadioic acid, hexadecadioic acid, eicosandioic acid, eicosadienedioic acid, 2,2 , 4-trimethyladipic acid and the like. Examples of diamines include ethylene diamine, trimethylene diamine, tetramethylene diamine, hexamethylene diamine, pentamethylene diamine, undecamethylene diamine, 2,2,4 (or 2,4,4) -trimethylhexamethylene diamine, cyclohexane diamine, Bis- (4,4′-aminocyclohexyl) methane, metaxylylenediamine, nonanediamine, decanediamine and the like can be mentioned.

  A polymer obtained by polycondensation of these or a copolymer thereof, such as nylon 6, 7, 11, 12, 6.6, 6.9, 6.11, 6.12, 6 / 6.6. 6/12 etc. can be used. In addition, when the biaxially stretched polyamide film of the present invention is produced, the above-described polyamide resin can be used alone, or two or more kinds can be mixed or multilayered. Of these, nylon 6 is preferred because of its excellent balance between heat resistance and mechanical properties.

  The relative viscosity of the aliphatic polyamide used in the present invention is 2.9 to 3.1, and preferably 2.95 to 3.05. If the relative viscosity of the aliphatic polyamide is less than 2.9, the tensile strength and impact strength are likely to decrease, and the melt viscosity becomes too low to form a sheet. If the relative viscosity of the aliphatic polyamide exceeds 3.1, the melt viscosity becomes high and is suitable for tubular simultaneous biaxial stretching. However, during tenter simultaneous biaxial stretching, the molten resin is filtered. In doing so, the pressure loss is large, extra extrusion energy is required, and the production cost increases. The relative viscosity here refers to a sample solution (liquid temperature 20 ° C.) in which aliphatic polyamide is dissolved in 96% sulfuric acid to a concentration of 1.0 g / dl, and a predetermined viscometer (for example, Ubbelohde viscosity). This is the value obtained when measured using

  Polymetaxylene adipamide (MXD6) used in the present invention is obtained by a polycondensation reaction of metaxylylenediamine and adipic acid. Moreover, what contained the paraxylylene adipamide component at 5 mass% or less may be sufficient.

  The biaxially stretched polyamide film of the present invention comprises a mixture of the aliphatic polyamide and polymetaxylene adipamide (MXD6). In the present invention, the mixing ratio of aliphatic polyamide and polymetaxylene adipamide (MXD6) is 80/20 to 99/1 (mass ratio) of aliphatic polyamide / polymetaxylene adipamide (MXD6). It is preferably 83/17 to 98/2 (mass ratio), more preferably 85/15 to 95/5 (mass ratio), and 88/12 to 93/7 (mass ratio). ) Is most preferred. If the content of polymetaxylene adipamide (MXD6) is less than 1% by mass, linear cutability will not be exhibited, and if it exceeds 20% by mass, the toughness and pinhole resistance of the resulting biaxially stretched polyamide film will decrease. Sometimes.

  In the biaxially stretched polyamide film of the present invention, generally known additives such as lubricants, anti-pinhole improvers, pigments, antioxidants, ultraviolet rays are used as long as the properties of the biaxially stretched polyamide film of the present invention are not impaired. Absorbers, preservatives, antistatic agents, inorganic fine particles and the like can be added.

The lubricant is used for imparting slipperiness to the obtained biaxially stretched polyamide film. For example, clay, talc, mica, calcium carbonate, zinc carbonate, wollastoniro, silica, alumina, magnesium oxide, calcium silicate, aluminum Inorganic lubricants such as sodium oxide, calcium aluminate, magnesium aluminosilicate, glass balloon, zinc oxide, antimony trioxide, zeolite, kaolinite, hydrotalcite, layered silicate, stearamide, behenamide, Elca Organic lubricants such as acid amide, ethylene bis stearic acid amide, phenol resin, melamine resin, and polymethyl methacrylate resin are listed. These lubricants may be used alone or in combination. Among these, silica is preferable because it has a high effect of improving slipperiness without impairing tearability and pinhole resistance.
Examples of the method of adding the lubricant include a method of adding particles in a polyamide resin as a raw material, a method of adding particles directly to an extruder, etc., and adopting one of these methods. Two methods may be used in combination.

  The anti-pinhole improver enhances pinhole resistance of the resulting biaxially stretched polyamide film, particularly durability against bending fatigue, and uses various resins such as polyolefins, polyamide elastomers, and polyester elastomers. be able to. The content of the anti-pinhole improver in the biaxially stretched polyamide film is arbitrary, but these anti-pinhole improvers impart flexibility to the base polyamide resin, and therefore are contained excessively. In such a case, the tearability of the biaxially stretched polyamide film is greatly impaired, and sufficient caution is required for use.

The biaxially stretched polyamide film of the present invention is obtained by using a film laminate obtained by laminating the biaxially stretched polyamide film to obtain a packaging bag, and then in the longitudinal direction (MD direction) when the biaxially stretched polyamide film is formed. ), And the width of the tear between the front and back surfaces of the film laminate when tearing 200 mm in the MD direction is 2.0 mm or less over the entire width of the biaxially stretched polyamide film. Preferably, it is 1.8 mm or less, more preferably 1.6 mm or less, and most preferably 1.4 mm or less.
Note that “over the entire width of the film” means the entire width of the original film unless otherwise specified. Further, the full width of the raw film excludes portions (so-called ear portions) that are not stretched at the ends of the film that are gripped during film stretching. That is, the maximum width of the portion where the film thickness falls within a predetermined range and can be shipped as a product is defined as the full width in the present application.

The packaging bag will be described.
When obtaining a packaging bag using the biaxially stretched polyamide film of the present invention, first, in order to impart heat sealability, an unstretched sealant film made of polyethylene and polypropylene is laminated to obtain a film laminate. As a lamination method, a known method such as dry lamination or extrusion lamination can be used. The biaxially stretched polyamide film may be printed in advance. Moreover, in order to improve printability and designability, other plastic films such as polyester or paper can be laminated and used. Furthermore, in order to provide gas barrier properties, an ethylene-vinyl acetate copolymer or a metal foil can be laminated, or a metal thin film or a gas barrier coating can be provided on any layer constituting the packaging bag. In this case, the biaxially stretched polyamide film of the present invention is used in at least one layer, and two or more layers of the biaxially stretched polyamide film of the present invention may be used as long as the linear cut property of the laminated film is not impaired.

  The film laminate can be folded in half and heat sealed at the end to form a packaging bag. The packaging bag is filled with the contents, and the opening is hermetically sealed so that it is distributed as a sealed packaging bag. After distribution, the sealed packaging bag is opened and the contents are taken out. What is important here is to make the film tearing direction of the opening of the sealed packaging bag coincide with the MD direction of the biaxially stretched polyamide film of the present invention. By doing in this way, it can be set as the packaging bag which the taking-out property of the content improved. In addition, when the biaxially stretched polyamide film of the present invention is used, since the gap width between the tear portion of the front surface and the back surface of the film laminate when tearing 200 mm in the MD direction is extremely small as a packaging bag, the linear cut property is sufficient. To improve.

  The method for producing the biaxially stretched polyamide film of the present invention will be described. As described above, the biaxially stretched polyamide film of the present invention is preferably manufactured using a stretching apparatus having a linear motor type tenter, but is not particularly limited to a linear motor type tenter.

  The biaxially stretched polyamide film of the present invention can be produced as follows. After the polyamide resin is melted by an extruder, it is extruded as a molten sheet from a T-die, and is brought into close contact with a cooling drum whose surface temperature is adjusted to 0 to 25 ° C. and rapidly cooled to obtain a continuous unstretched sheet.

  Prior to biaxial stretching of the unstretched film, the unstretched film is sent to a hot water tank adjusted to 20 to 80 ° C. and subjected to humidity conditioning for 10 minutes or less. This treatment is for preventing the film from being cut in the stretching step, and the humidity can be appropriately plasticized to suppress crystallization.

  The unstretched film may be subjected to water absorption treatment so that the moisture content is 3.0 to 7.0% by mass, preferably 4.0 to 6.0% by mass, and then simultaneously biaxially stretched in the longitudinal and lateral directions. preferable. When the water absorption is less than 3.0% by mass, the stretching stress increases, troubles such as cutting occur, and the operability is lowered. When the water absorption is greater than 7.0% by mass, the resulting biaxial structure is obtained. The strength of the stretched polyamide film decreases, and the thickness unevenness of the film in the width direction increases. On the other hand, if the water absorption rate is too large, the unstretched film being subjected to the water absorption treatment is folded and wrinkled, and troubles such as meandering of the film are likely to occur.

  The unstretched film subjected to the water absorption treatment is preheated at a temperature of 200 to 230 ° C., more preferably 215 to 225 ° C., and then subjected to simultaneous biaxial stretching at a temperature of 200 to 230 ° C., more preferably 215 to 225 ° C. Do. In general, the draw ratio is preferably 2.5 times or more in the machine direction (MD direction) and the transverse direction (TD direction), and the length x transverse draw ratio is preferably 7 times or more. In addition, the MD direction draw ratio and the TD direction draw ratio are preferably MD direction / TD direction ≧ 0.91, more preferably MD direction / TD direction ≧ 0.93, MD direction / More preferably, the TD direction ≧ 0.95. By setting the stretch ratio as described above, the tearability can be improved by increasing the orientation of MXD6 in the obtained biaxially stretched polyamide film. Furthermore, even if the content of polymetaxylene adipamide (MXD6) used is small, the tearability is improved as compared with the conventional biaxially stretched polyamide film. In addition, pinhole resistance, in particular, bending pinhole resistance, can be improved.

  Next, the biaxially stretched polyamide film is preferably heat-treated at a temperature of 200 to 215 ° C. When the heat treatment temperature is lower than 200 ° C., it becomes difficult to make the heat shrinkage rate less than 2.0% when treated with boiling water at 100 ° C. for 5 minutes even if the relaxation treatment described later is performed. When the heat treatment temperature is higher than 215 ° C., the impact resistance and transparency of the resulting biaxially stretched polyamide film are lowered, which is not preferable.

  Subsequently, in the zone immediately after the heat treatment, the relaxation rate (T) in the TD direction is 1% ≦ T ≦ 10%, preferably 1% ≦ T ≦ 5%, and 190 to 215 ° C. for 1 to 10 seconds. It is preferable to apply a relaxation treatment. When the relaxation rate exceeds 10%, productivity and mechanical properties of the biaxially stretched polyamide film are deteriorated, which is not preferable. Further, if the relaxation rate is less than 1%, it is difficult to sufficiently reduce the thermal shrinkage rate, and the balance between the thermal shrinkage rates in the MD direction and the TD direction is deteriorated, which is not preferable.

  Before and after the TD relaxation step, the relaxation rate (M) in the MD direction is 1% ≦ M ≦ 10%, preferably 1% ≦ M ≦ 5%, and a relaxation treatment is performed at 190 to 215 ° C. for 1 to 10 seconds, A biaxially stretched polyamide film is used. When the relaxation rate exceeds 10%, productivity and mechanical properties of the biaxially stretched polyamide film are deteriorated, which is not preferable. Further, if the relaxation rate is less than 1%, it is difficult to sufficiently reduce the thermal shrinkage rate, and the balance between the thermal shrinkage rates in the MD direction and the TD direction is deteriorated, which is not preferable.

The thickness of the biaxially stretched polyamide film of the present invention is not particularly limited, but is preferably 6 to 25 μm, and more preferably 12 to 25 μm. When the thickness is less than 6 μm, the pinhole resistance of the biaxially stretched polyamide film is impaired. When the thickness exceeds 25 μm, the tearability may not be sufficiently exhibited.

  Further, a single layer or a multilayer of two or more layers may be used as long as the requirements of the present invention are satisfied.

  The biaxially stretched polyamide film of the present invention may be subjected to a discharge treatment such as a corona discharge treatment as long as it does not impair the effects of the present invention.

  Since the biaxially stretched polyamide film of the present invention is excellent in linear cut property, it can be suitably used as a packaging bag used in various packaging applications. In addition, since the pinhole resistance is improved, it can be used as a base film for foods, pharmaceuticals, industrial products, etc., and the openability can be improved while improving the content protection.

  The present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Production Example 1
<Production of film laminate>
About the biaxially stretched polyamide film obtained in the examples or comparative examples described later, an aromatic ester adhesive (Dick Dry LX500 / KR90S manufactured by DIC Graphics) is applied to the corona-treated surface of each biaxially stretched polyamide film. The applied film was dried with a hot air drier at 80 ° C. for 10 seconds so that the adhesive application amount was 3 g / m ² . The adhesive-coated surface and the corona-treated surface of a sealant film (RXC-22 manufactured by Mitsui Chemicals, Inc., non-stretched polypropylene film with a thickness of 50 μm) are bonded together, and aged for 72 hours in an atmosphere of 40 ° C., biaxially stretched polyamide film / The film laminated body which consists of two layers of a sealant film was obtained.

Production Example 2
<Production of packaging bag>
Using the film laminate obtained in Production Example 1, half-folded so that the MD direction of the biaxially stretched polyamide film becomes the length of the packaging bag so as to have a shape as shown in FIG. A three-sided bag (length 300 × width 200 mm, seal width 10 mm) was obtained, and a notch 3 of 5 mm was provided in the side seal portion as shown in FIG. The heat sealing was performed at a sealing temperature of 180 ° C., a sealing pressure of 0.29 MPa, and a sealing time of 1 second.

<Straight line cut evaluation>
In the three-sided bag obtained in Production Example 2, the width shifted from the straight line drawn in the longitudinal direction from the notch notch was measured by tearing 100 mm in the right front and left front directions from the notch provided in the side seal portion. This operation was repeated 5 times, and the average value was calculated. When the straight line was drawn in the longitudinal direction and the absolute value of the deviation amount from the straight line when it was torn 200 mm was evaluated as ◯ and 2.0 mm or less, it was evaluated as x.

<Flexible pinhole resistance>
A 200 mm x 300 mm biaxially stretched polyamide film raw material (hereinafter referred to as a test film) conditioned under conditions of 20 ° C x 65% RH is attached to a gelboflex tester (manufactured by Tester Sangyo Co., Ltd.) The sample was rotated 440 °, further moved straight by 64 mm, and thereafter the movement until returning to the original position in the reverse process was counted as one, and 10,000 bending tests were performed. For the test film after the bending test, a colored liquid (ageless checker manufactured by Mitsubishi Gas Chemical Co., Ltd.) was applied to one side of the test film, and the number of pinholes penetrating the colored liquid on the opposite side was defined as the number of pinholes.

Example 1
Polyamide 6 (Unitika A1030BRF) and MXD6 (Mitsubishi Engineering Plastics) were dried, mixed to give polyamide 6 / MXD6 = 80/20 (mass ratio), and then charged into an extruder, and heated to 260 ° C. After melting in the cylinder, it was melt-extruded into a sheet form from a T-die, wound around a metal drum adjusted to 20 ° C. and cooled to obtain an unstretched sheet having a thickness of 150 μm. This unstretched sheet was sent to a hot water tank adjusted to 60 ° C. and immersed for 1 minute, so that the moisture content of the unstretched sheet was 4.0%. Next, the end of this unstretched sheet is held by a linear motor type tenter clip, and simultaneously biaxially stretched at a stretching ratio of 3.0 times in the MD direction and 3.3 times in the TD direction under the condition of 180 ° C. After that, heat treatment was performed at 201 ° C. for 4 seconds with a relaxation rate in the TD direction of 5%, and gradually cooled to room temperature to obtain a biaxially stretched polyamide film having a width of 2300 mm and a thickness of 15 μm. Various evaluation was performed about the obtained biaxially stretched polyamide film. The results are shown in Table 1.

Examples 2 to 23, Comparative Examples 1 and 2
A biaxially stretched polyamide film was obtained in the same manner as in Example 1 except that the draw ratio as described in Tables 1 and 2 and the mixing ratio of polyamide 6 and MXD6 were used, and various evaluations were performed. In addition, although Example 1, 20, and 21 are the biaxially stretched polyamide films obtained on the same conditions, the positions of the original fabric in various evaluation differ. That is, Example 21 is a biaxially stretched polyamide film sampled at a center portion in the TD direction, Example 20 is sampled at a position 500 mm from the center, and Example 1 is sampled at a position 1000 mm from the center. Similarly, Examples 11, 22, and 23 are biaxially stretched polyamide films obtained under the same conditions, and the taking positions are different. The results are shown in Tables 1 and 2.

Comparative Example 3, Examples 24 and 25
A biaxially stretched polyamide film was obtained in the same manner as in Example 1 except that the stretching method was pantograph simultaneous biaxial stretching. These are different from each other in the position of taking the original fabric. The results are shown in Table 2.

  In Examples 1 to 25, a biaxially stretched polyamide film having a predetermined tear performance was obtained. Such a biaxially stretched polyamide film was also excellent in pinhole resistance.

  In Comparative Example 1, MXD6 was not mixed and used, so that tearability was poor.

  In Comparative Example 2, the tearability and pinhole resistance were inferior.

  In Comparative Example 3, the tearability was inferior.

1. Packaging bag2. Bonding part 3. Notch part 4. Edge (film body)
5. Seal (film edge

Claims (6)

  A biaxially stretched polyamide film comprising a mixture of aliphatic polyamide and polymetaxylene adipamide (MXD6), and after obtaining a packaging bag using a film laminate obtained by laminating the biaxially stretched polyamide film, When the biaxially stretched polyamide film is cut in the longitudinal direction (MD direction), the gap width between the tear portions of the front and back surfaces of the film laminate when it is torn 200 mm in the MD direction is 2.0 mm or less. A biaxially stretched polyamide film characterized by that.   The mixing ratio of aliphatic polyamide and polymetaxylene adipamide (MXD6) is aliphatic polyamide / polymetaxylene adipamide (MXD6) = 80/20 to 99/1 (mass ratio) The biaxially stretched polyamide film according to claim 1.   The method for producing a biaxially stretched polyamide film according to claim 1 or 2, wherein the unstretched film is simultaneously biaxially stretched at a longitudinal stretching ratio of 2.5 times or more and at a longitudinal x lateral stretching ratio of 7 times or more.   The method for producing a biaxially stretched polyamide film according to claim 3, wherein a stretching ratio in the machine direction (MD direction) and a stretching ratio in the transverse direction (TD direction) are MD direction / TD direction ≧ 0.91.   The method for producing a biaxially stretched polyamide film according to claim 3 or 4, wherein the tenter is driven by a linear motor system. A packaging bag using the biaxially stretched polyamide film according to claim 1.